On Tue, Jul 09, 2013 at 09:23:10AM -0400, Jeff Layton wrote:
> On Wed, 3 Jul 2013 16:12:33 -0400
> "J. Bruce Fields" <bfields@xxxxxxxxxx> wrote:
>
> > From: "J. Bruce Fields" <bfields@xxxxxxxxxx>
> >
> > We'll need the same logic for rename and link.
> >
> > Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
> > ---
> > fs/namei.c | 13 +++----------
> > include/linux/fs.h | 33 +++++++++++++++++++++++++++++++--
> > 2 files changed, 34 insertions(+), 12 deletions(-)
> >
> > diff --git a/fs/namei.c b/fs/namei.c
> > index cba3db1..a9d4031 100644
> > --- a/fs/namei.c
> > +++ b/fs/namei.c
> > @@ -3401,14 +3401,9 @@ int vfs_unlink(struct inode *dir, struct dentry *dentry, struct inode **delegate
> > else {
> > error = security_inode_unlink(dir, dentry);
> > if (!error) {
> > - error = break_deleg(target, O_WRONLY|O_NONBLOCK);
> > - if (error) {
> > - if (error == -EWOULDBLOCK && delegated_inode) {
> > - *delegated_inode = target;
> > - ihold(target);
> > - }
> > + error = try_break_deleg(target, delegated_inode);
> > + if (error)
> > goto out;
> > - }
> > error = dir->i_op->unlink(dir, dentry);
> > if (!error)
> > dont_mount(dentry);
> > @@ -3478,9 +3473,7 @@ exit2:
> > iput(inode); /* truncate the inode here */
> > inode = NULL;
> > if (delegated_inode) {
> > - error = break_deleg(delegated_inode, O_WRONLY);
> > - iput(delegated_inode);
> > - delegated_inode = NULL;
> > + error = break_deleg_wait(&delegated_inode);
> > if (!error)
> > goto retry_deleg;
> > }
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index f951588..c37e463 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -1894,6 +1894,9 @@ extern bool our_mnt(struct vfsmount *mnt);
> >
> > extern int current_umask(void);
> >
> > +extern void ihold(struct inode * inode);
> > +extern void iput(struct inode *);
> > +
> > /* /sys/fs */
> > extern struct kobject *fs_kobj;
> >
> > @@ -1962,6 +1965,28 @@ static inline int break_deleg(struct inode *inode, unsigned int mode)
> > return 0;
> > }
> >
> > +static inline int try_break_deleg(struct inode *inode, struct inode **delegated_inode)
> > +{
> > + int ret;
> > +
> > + ret = break_deleg(inode, O_WRONLY|O_NONBLOCK);
> > + if (ret == -EWOULDBLOCK && delegated_inode) {
> > + *delegated_inode = inode;
> > + ihold(inode);
> > + }
> > + return ret;
> > +}
> > +
>
> Actually, now that I look...
>
> Suppose a vfs_unlink caller passes in a NULL delegated_inode pointer.
> He'll get back a -EWOULDBLOCK here if there's a delegation on it.
> Presumably he'll just treat that as a hard error and the delegation
> would never get broken. Is that expected?
Yes.
The callers that pass in NULL are callers who should really never
encounter a write delegation. E.g. it might happen if you exported a
filesystem that you're also stacking ecryptfs on top of (assuming that's
possible). Maybe I'm missing something, but that looks pointless.
Erroring out seems a safe way to handle it.
It wouldn't be a problem to convert more of those callers to do the same
retry loop, it just seems better to avoid the extra spaghetti to support
what looks like a nutty use case.
--b.
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